Principles of antibiotic therapy.

Many host factors influence both the presentation and response to therapy of clinical infections. Since the selection of an appropriate antibiotic depends significantly upon results of in vitro susceptibility testing, great care should be taken to obtain suitable specimens for culture and susceptibility studies. The likelihood that antibiotic therapy will be successful depends upon whether the drug will reach the infected site at the desired concentration and for an optimal duration of time. Local factors such as pH, oxygen tension, and the presence of inactivating substances may affect antibiotic activity. At present, many of our recommendations for dose, dosage intervals, and duration of therapy are largely empiric. Enhanced understanding of the pharmacokinetics of antimicrobial agents should provide the basis for more rational therapy in the future. The remainder of this symposium will present the data from which such recommendations can be drawn.